Multi-stage adhesion structure facing macro-micro-nano cross-scale rough surface and forming method of multi-stage adhesion structure

Abstract

The invention discloses a multi-stage adhesion structure facing a macro-micro-nano cross-scale rough surface and a forming method of the multi-stage adhesion structure. The multi-stage adhesion structure comprises a top adhesion fiber layer, a middle backing layer and a bottom supporting layer which are sequentially arranged from top to bottom. A bottom supporting layer is composed of a bottom pole plate and a substrate polymer film connected to the bottom pole plate; the middle-layer polar plate forms a middle backing layer; the bottom polymer film and the top polymer film outside the bottom polymer film form a top adhesive fiber layer; during forming, a top-layer polar plate, a middle-layer polar plate and a forming polymer material are treated in sequence, and a bottom-layer polar plate and a substrate polymer material are treated; then electric field induced rheological forming of the adhesion structure is carried out, and finally curing and demolding of the polymer are carried out. The contact and adhesion effects on an uneven surface and a microcosmic rough surface are improved, and the efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of bionic adhesion functional structures in micro-nano engineering, and in particular relates to a multi-level adhesion structure facing a macro-micro-nano cross-scale rough surface and a forming method thereof. Background Art

[0002] Nature has endowed geckos with the ability to crawl on walls, and the mechanism behind this has been elucidated by scholars. Studies have shown that the adhesion system of gecko feet can form good contact with the wall, thereby generating van der Waals forces, which manifest as adhesion to the surface on a macro scale. Compared with traditional chemical adhesion and mechanical locking, bionic adhesion has excellent characteristics such as good repeatability, no residue on the adhered surface, and insensitivity to the morphology and material of the adhered surface. In view of these advantages, in recent years, dry adhesion functional surfaces prepared by imitating the complex micro-nanostructure of gecko feet have been widely used in many fields such as medical care, bionic robots and manipulators.

[0003] Previous studies have shown that mushroom-shaped microcolumn arrays with terminal swelling features similar to those of gecko bristles exhibit excellent adhesion properties on smooth surfaces. However, due to process limitations, the depth-to-width ratio of the bionic adhesive microcolumn structures currently produced is relatively low, and it is difficult to adapt to the adhered surfaces of different morphologies through deformation, resulting in the adhesion effect of the adhesive structure on curved surfaces and rough surfaces being far different from that on smooth surfaces. In order to achieve better conformal contact, some scholars have proposed a series of solutions, mainly divided into optimizing the fiber stiffness distribution and manufacturing multi-level structures. In 2017, the bionic adhesive fiber array with composite stiffness prepared by Dirk-M. Drotlef's team successfully achieved stable adhesion on soft, rough and skin surfaces. In addition to optimizing the stiffness of the fiber structure, scholars have also noticed the influence of structures other than the spatula-shaped bristles on the gecko's feet, such as soft flaps, on the gecko's crawling process. In 2019, Jamie A. Booth analyzed the adhesion performance of micro-pillar arrays with different backing thicknesses on the target surface of macroscopic angle errors. The experimental results showed that thick backing dry glue is more robust in the face of angle errors.

[0004] But in general, the existing structural forms or process solutions have certain shortcomings and cannot take into account the performance of microscopic surfaces or macroscopic non-aligned surfaces. In fact, the excellent crawling ability of geckos is inseparable from the synergistic effect of the adhesion structure and joints of their feet. Therefore, the multi-level structure with joint substrate and soft-hard composite adhesion end is a feasible solution to make the bionic adhesion structure take into account the adhesion performance of microscopic rough surfaces and macroscopic uneven surfaces. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned existing structures, the purpose of the present invention is to provide a multi-level adhesion structure and a forming method thereof for macro-micro-nano cross-scale rough surfaces, and the multi-level adhesion structure has good adhesion performance on macro-micro-nano cross-scale rough surfaces.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A multi-level adhesion structure facing a macro-micro-nano scale rough surface comprises a top adhesion fiber layer, an intermediate backing layer and a bottom support layer arranged in sequence from top to bottom; the bottom support layer is composed of a bottom electrode plate 7 and a substrate polymer film 6 connected thereto; the middle electrode plate 5 constitutes the middle backing layer; the bottom polymer film 4 and the top polymer film 3 outside it constitute the top adhesion fiber layer.

[0008] For the smooth target surface and the microscopically rough target 12 surface, the top polymer film 3 of the top adhesion fiber layer forms a good conformal contact with the target 12 surface, and the bottom polymer film 4 has the effect of inhibiting interface separation;

[0009] For the uneven surface of the target 12 on a macro scale, the middle backing layer and the bottom support layer will produce adaptive deformation to increase the contact area between the top adhesive fiber layer and the surface of the target 12; the middle backing layer evenly distributes the contact interface stress distribution to inhibit crack propagation.

[0010] The material of the bottom polymer film 4 is an elastomeric polymer with low rigidity after curing.

[0011] The material of the top polymer film 3 is an elastomeric polymer having high rigidity after curing.

[0012] The material of the substrate polymer film 6 is an elastomeric polymer having low rigidity after curing.

[0013] The method for forming a multi-level adhesion structure facing a macro-micro-nano cross-scale rough surface comprises the following steps:

[0014] 1) Treatment of the top electrode plate: a conductive plate with a flat surface is selected as the top electrode plate 1, and then a low surface energy film 2 is prepared on the top electrode plate 1;

[0015] 2) Preparation and treatment of the middle layer plate and the top adhesive fiber layer: The middle layer plate 5 uses a double-sided conductive plate, and a bottom polymer film 4 with a thickness of micrometer level is formed on the upper side of the middle layer plate 5 by a hot pressing process. After cooling, the bottom polymer film 4 is plasma cleaned; after the treatment is completed, a top polymer film 3 is prepared on the bottom polymer film 4 by a spin coating process, thereby forming a composite film on the middle layer plate 5;

[0016] 3) Processing of bottom electrode plate and substrate material: The bottom electrode plate 7 is a single-sided conductive plate of the same material and specification as the top electrode plate 1; a substrate polymer film 6 with a thickness of millimeters is prepared on the bottom electrode plate 7 by spin coating;

[0017] 4) Electric field induced rheological forming of multi-level adhesion structure: the top electrode plate 1, the middle electrode plate 5 and the bottom electrode plate 7 are arranged in parallel from top to bottom under dielectric support to form two capacitors; the top capacitor and the bottom capacitor are respectively connected to the first DC power supply 9 and the second DC power supply 10, the conductive side of the top electrode plate 1 is connected to the positive electrode of the first DC power supply 9, the conductive side of the bottom electrode plate 7 is connected to the positive electrode of the second DC power supply 10, the upper side of the middle electrode plate is connected to the negative electrode of the first DC power supply 9, and the lower side is connected to the negative electrode of the second DC power supply 10; the voltage is adjusted respectively, so that the polymer films in the top capacitor and the bottom capacitor will undergo rheology to form a microstructure array with the most unstable wavelength as the periodic size; the voltage is kept stable so that the microstructure array continues to grow upward; when the microstructure array is in contact with the middle electrode plate 5 and the top electrode plate 1, a stable voltage is continued to be applied, and the microstructure array eventually forms a "mushroom-shaped" end with a diameter slightly larger than the supporting column;

[0018] 5) Curing and demolding of the polymer: The voltage is continuously applied until the top polymer film 3 and the substrate polymer film 6 are completely cured, and the top electrode 1 is removed. After removing the dielectric support, a multi-level adhesion structure with cross-scale surface adhesion performance is obtained.

[0019] In the step 3), when the substrate polymer film 6 is spin-coated, a support with a thickness of millimeters around the electrode is required to assist in film formation.

[0020] In the step 4), the thickness of the dielectric support is greater than the thickness of the polymer film. The thickness of the first dielectric support 8 of the top capacitor is 1.5-3 times the thickness of the bottom polymer film 4 h1 + the thickness of the top polymer film 3 h2. The thickness H of the second dielectric support 11 in the bottom capacitor is 1.5-3 times the thickness H1 of the substrate polymer film 6.

[0021] In the step 5), the top polymer film 3 and the substrate polymer film 6 are cured by ultraviolet light curing or thermal curing.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention is not limited to the conventional homogeneous single-layer adhesion structure that adapts to the target surface morphology through the deformation of a single adhesion fiber. It combines the method of improving the stiffness distribution of the adhesion fiber and adding a discrete flexible backing support, which greatly improves the contact and adhesion effects of rough surfaces and uneven surfaces, while also having excellent adhesion properties of anti-overturning and anti-vibration.

[0024] The present invention adopts electric field induced forming process to prepare multi-level adhesion structure, which has significant process advantages and application value, and has the following characteristics: the process is simple, no expensive equipment and complex control are required, and the production cost is effectively reduced; the processing efficiency is high and suitable for large-scale production; the prepared multi-level adhesion structure has excellent cross-scale surface adaptability. Based on these characteristics, this technology shows broad application prospects in the fields of industrial picking, space grabbing, flexible devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the cross section of the top electrode plate in the embodiment of the present invention.

[0026] Figure 2 It is a cross-sectional schematic diagram of preparing a composite material film on an intermediate layer electrode plate according to an embodiment of the present invention.

[0027] Figure 3 It is a cross-sectional schematic diagram of preparing a substrate material film on a bottom electrode plate according to an embodiment of the present invention.

[0028] Figure 4 Schematic diagram of applying an external electric field to perform double-layer electro-induced rheology forming according to an embodiment of the present invention.

[0029] Figure 5 Schematic diagram of structural rheology when electric field is induced without contacting the dielectric layer according to an embodiment of the present invention.

[0030] Figure 6 Schematic diagram of structural rheology after electric field induced contact with dielectric layer according to an embodiment of the present invention.

[0031] Figure 7 This is a schematic diagram of a multi-level adhesion structure facing a macro-micro-nano cross-scale rough surface obtained by removing the upper electrode plate after curing in an embodiment of the present invention.

[0032] Figure 8 Schematic diagram of the adhesion enhancement principle of the multi-level adhesion structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with embodiments and drawings, but the protection scope of the present invention is not limited thereto.

[0034] Embodiment, a method for forming a multi-level adhesion structure on a macro-micro-nano cross-scale rough surface, comprising the following steps:

[0035] 1) Treatment of the top plate: refer to Figure 1 , a conductive plate with a flat surface is selected as the top electrode plate 1, a PTFE solution with a volume fraction of 20% is spin-coated on the surface of the top electrode plate 1, and after the spin coating is completed, it is cured at a temperature of 100° C. for 20 minutes to obtain a low surface energy film 2 with a thickness of micrometer level;

[0036] 2) Preparation and treatment of the intermediate layer plate and the top adhesive fiber layer: refer to Figure 2 , the middle layer electrode 5 is a double-sided conductive ITO glass plate with the same length and width as the top layer electrode; then the thermoplastic polymer is placed on the surface of the middle layer electrode 5, heated to restore the fluidity of the thermoplastic polymer, and another hydrophobic glass is covered on the upper side of the thermoplastic polymer and uniform pressure is applied, and after the thermoplastic polymer film is solidified, the hydrophobic glass is removed to obtain a bottom polymer film 4 with a thickness of h1; in order to increase the affinity between the bottom polymer film 4 and the top polymer film 3, the bottom polymer film 4 needs to be treated with oxygen plasma cleaning for 5 minutes; finally, the top polymer is placed on the surface of the plasma-cleaned bottom polymer film 4, and spin-coated to obtain a top polymer film 3 with a thickness of h2;

[0037] 3) Preparation of bottom plate and substrate materials: refer to Figure 3 The bottom electrode 7 is a single-sided conductive plate of the same material and specification as the top electrode 1 in step 1); the substrate material is a thermosetting silicone rubber with a Shore hardness of about 10, and a substrate polymer film 6 with a thickness of H1 is obtained on the surface of the bottom electrode 7 by a spin coating process. It should be noted that during spin coating, tape or the like is used as a support to form a closed rectangular space around the bottom electrode 7 to assist in the formation of a millimeter-scale polymer film during and after the spin coating process;

[0038] 4) Electric field induced rheological forming of multi-level adhesion structure: reference Figure 4 The top plate 1, the middle plate 5 and the bottom plate 7 are arranged in parallel from top to bottom under the dielectric support to form two capacitors. The dielectric support should be made of high temperature resistant and good insulating materials. In order to leave enough space for the polymer growth and not to weaken the electric field force too much, the dielectric support should be of appropriate thickness. Generally speaking, the thickness h of the first dielectric support 8 in the top capacitor should be within the range of 1.5 to 3 times the total thickness of the bottom polymer film 4 thickness h1 + the top polymer film 3 thickness h2. Similarly, the thickness H of the second dielectric support 11 in the bottom capacitor should also be within the range of 1.5 to 3 times the thickness H1 of the substrate polymer film 6. For the top capacitor and the bottom The layer capacitors are respectively connected to a first DC power source 9 and a second DC power source 10, wherein the voltage of the first DC power source 9 should be controlled within the range of 400V to 1000V, and the voltage adjustment range of the second DC power source 10 is 4000V to 6000V; the conductive side of the top plate 1 is connected to the positive electrode of the first DC power source 9, the conductive side of the bottom plate 7 is connected to the positive electrode of the second DC power source 10, the upper side of the middle layer plate is connected to the negative electrode of the first DC power source 9, and the lower side is connected to the negative electrode of the second DC power source 10; under the action of the electric field force at the gas / liquid and liquid / liquid interfaces, the polymer films in the top capacitor and the bottom capacitor will undergo rheology to form a microstructure array with the most unstable wavelength as the periodic size, such as Figure 5As shown; the microstructure array continues to grow upward until its height is equal to the thickness of the dielectric support. When the microstructure array contacts the middle layer electrode 5 and the top layer electrode 1, a stable voltage is continuously applied. The electric field force acting at the three-phase boundary (solid / liquid / gas) will cause the polymer material to expand in all directions, eventually forming a "mushroom-shaped" end with a diameter slightly larger than the support column, as shown in FIG. Figure 6 As shown;

[0039] 5) Curing and demolding of polymers: During the initial rheological process of the top polymer film 3 and the substrate polymer film 6 until they are completely cured, they should be kept warm at a certain temperature to meet the fluidity conditions of the thermoplastic polymer and the curing conditions of the thermosetting polymer; the heat source can be an electric heating blast drying oven, an electric heating table, etc.; after the top polymer film 3 and the substrate polymer film 6 are completely cured, cool for 30 minutes to solidify the bottom polymer film 4, remove the top electrode 1, and remove the dielectric support to obtain a multi-level adhesion structure with cross-scale adhesion properties, such as Figure 7 shown.

[0040] The above-mentioned forming method can realize the size-controllable manufacturing of cross-scale surface adhesion structure, wherein the thickness H of the substrate polymer film 6 is directly controlled by the second dielectric support 11; when the thickness H of the substrate polymer film 6 remains unchanged, the period gap L and diameter D of the microstructure array formed by the substrate polymer film 6 are controlled by the voltage of the second DC power supply 10, and the larger the voltage of the second DC power supply 10, the smaller the period gap L and the diameter D; the top polymer film 3 also has a similar control rule: the larger the voltage of the first DC power supply 9, the smaller the fiber gap l and the fiber diameter d1 of the microstructure array formed by the top polymer film 3; when the same low surface energy material 2 is used to prepare the top electrode, the fiber end diameter d2 is mainly controlled by the electrowetting time, that is, the power-on time before the polymer solidifies, and the longer the power-on time, the larger the end diameter.

[0041] Reference Figure 8 The multi-level adhesion structure facing the macro-micro-nano cross-scale rough surface comprises a top adhesion fiber layer, an intermediate backing layer and a bottom support layer arranged in sequence from top to bottom; the bottom support layer is composed of a bottom electrode plate 7 and a substrate polymer film 6 connected thereto; the middle electrode plate 5 constitutes the middle backing layer; the bottom polymer film 4 and the top polymer film 3 outside thereof constitute the top adhesion fiber layer;

[0042] For smooth target surfaces and microscopically rough target 12 surfaces, the top polymer film 3 of the top adhesive fiber layer can form good conformal contact with the target 12 surface, while the bottom polymer film 4 has the effect of inhibiting interface separation;

[0043] For the uneven surface of the target 12 on a macro scale, the middle backing layer and the bottom support layer will produce adaptive deformation to increase the contact area between the top adhesive fiber layer and the surface of the target 12; the middle backing layer evenly distributes the contact interface stress distribution to inhibit crack propagation.

[0044] The present invention is not limited to the conventional homogeneous single-layer adhesion structure that adapts to the target surface morphology through the deformation of a single adhesion fiber. It combines the method of improving the stiffness distribution of the adhesion fiber and adding a discrete flexible backing support, which greatly improves the contact and adhesion effects of rough surfaces and uneven surfaces. At the same time, it has excellent adhesion properties of anti-overturning and anti-vibration. It has broad application prospects in vacuum picking, industrial handling, flexible electronics, and dexterous hand attachment.

[0045] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A multi-level adhesion structure for macro-micro-nano cross-scale rough surfaces, characterized by: The invention comprises a top adhesive fiber layer, an intermediate backing layer and a bottom support layer which are arranged in sequence from top to bottom; the bottom support layer is composed of a bottom electrode plate (7) and a substrate polymer film (6) connected thereto; the middle electrode plate (5) constitutes the middle backing layer; and the bottom polymer film (4) and the top polymer film (3) outside thereof constitute the top adhesive fiber layer.

2. The multi-stage adhesive structure according to claim 1, characterized in that: For the smooth target surface and the microscopically rough target (12) surface, the top polymer film (3) of the top adhesive fiber layer forms a good conformal contact with the target (12) surface, and the bottom polymer film (4) has the effect of inhibiting interface separation; For a target (12) surface that is uneven on a macroscopic scale, the middle backing layer and the bottom support layer will produce adaptive deformation to increase the contact area between the top adhesive fiber layer and the target (12) surface; the middle backing layer evenly distributes the contact interface stress distribution to inhibit crack propagation.

3. The multi-stage adhesive structure according to claim 1, characterized in that: The material of the bottom polymer film (4) is an elastomeric polymer with low rigidity after curing.

4. The multi-stage adhesive structure according to claim 1, characterized in that: The material of the top polymer film (3) is an elastomeric polymer having high rigidity after curing.

5. The multi-stage adhesive structure according to claim 1, characterized in that: The material of the substrate polymer film (6) is an elastomeric polymer with low rigidity after curing.

6. A method for forming a multi-level adhesion structure facing a macro-micro-nano cross-scale rough surface according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Treatment of the top electrode plate: a conductive plate with a flat surface is selected as the top electrode plate (1), and then a low surface energy film (2) is prepared on the top electrode plate (1); 2) Preparation and treatment of the intermediate electrode plate and the top adhesive fiber layer: The intermediate electrode plate (5) is a double-sided conductive plate, and a bottom polymer film (4) with a thickness of micrometer level is formed on the upper side of the intermediate electrode plate (5) by a hot pressing process. After cooling, the bottom polymer film (4) is subjected to a plasma cleaning process; after the treatment is completed, a top polymer film (3) is prepared on the bottom polymer film (4) by a spin coating process, thereby forming a composite film on the intermediate electrode plate (5); 3) Processing of the bottom electrode plate and substrate materials: The bottom electrode plate (7) is a single-sided conductive plate with the same material and specification as the top electrode plate (1); a substrate polymer film (6) with a thickness of millimeters is prepared on the bottom electrode plate (7) by spin coating; 4) Electric field induced multi-level adhesion structure rheological forming: the top electrode plate (1), the middle electrode plate (5) and the bottom electrode plate (7) are arranged in parallel from top to bottom under dielectric support to form two capacitors; The top layer capacitor and the bottom layer capacitor are respectively connected to a first DC power source (9) and a second DC power source (10); the conductive side of the top layer plate (1) is connected to the positive electrode of the first DC power source (9); the conductive side of the bottom layer plate (7) is connected to the positive electrode of the second DC power source (10); the upper side of the middle layer plate is connected to the negative electrode of the first DC power source (9); and the lower side is connected to the negative electrode of the second DC power source (10); the voltage is adjusted respectively so that the polymer films in the top layer capacitor and the bottom layer capacitor will undergo rheology to form a microstructure array with the most unstable wavelength as the periodic size; the voltage is kept stable so that the microstructure array continues to grow upward; when the microstructure array contacts the middle layer plate (5) and the top layer plate (1), a stable voltage is continuously applied so that the microstructure array eventually forms a "mushroom-shaped" end with a diameter slightly larger than that of the supporting column; 5) Curing and demolding of the polymer: voltage is continuously applied until the top polymer film (3) and the substrate polymer film (6) are completely cured, and the top electrode (1) is removed. After removing the dielectric support, a multi-level adhesion structure with cross-scale surface adhesion properties is obtained.

7. The forming method according to claim 6, characterized in that: In the step 3), when the substrate polymer film (6) is spin-coated, a support with a thickness of millimeters around the electrode plate is required to assist in film formation.

8. The forming method according to claim 6, characterized in that: In the step 4), the thickness of the dielectric support is greater than the thickness of the polymer film, the thickness of the first dielectric support (8) of the top capacitor is 1.5-3 times the total thickness of the bottom polymer film (4) thickness h1 + the top polymer film (3) thickness h2, and the thickness H of the second dielectric support (11) in the bottom capacitor is 1.5-3 times the thickness H1 of the substrate polymer film (6).

9. The forming method according to claim 6, characterized in that: In the step 5), the top polymer film (3) and the substrate polymer film (6) are cured by ultraviolet light curing or thermal curing.

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